Method and an apparatus for encoding/decoding residual coefficient

ABSTRACT

The encoding/decoding method and apparatus according to the present invention derives a residual coefficient of a residual block, calculates a quantization parameter for a residual block, performs dequantization on a residual coefficient using a quantization parameter, and performs inverse transform on a dequantized residual coefficient to reconstruct a residual sample of a residual block.

RELATED APPLICATION

This application claims priority to Korean Application 10-2018-0070161,filed on Jun. 19, 2018, which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding a video signal.

BACKGROUND

The demand for high resolution, high quality video is increasing invarious applications. As the image data becomes high resolution and highquality, the data amount increases relative to the conventional imagedata. Therefore, when image data is transmitted using a medium such as aconventional wired/wireless broadband line or is stored using aconventional storage medium, the transmission cost and the storage costare increased. High-efficiency image compression techniques may beutilized to solve these problems caused by the high resolution and highquality of image data.

SUMMARY

An object of the present invention is to improve encoding/decodingefficiency of residual blocks.

An object of the present invention is to improve encoding/decodingefficiency through adaptive block division.

A video encoding/decoding method and apparatus according to the presentinvention may derive a residual coefficient of a residual block,calculate a quantization parameter for the residual block, performdequantization on the residual coefficient using the calculatedquantization parameter for the residual block, and perform inversetransform on the dequantized residual coefficient to reconstruct aresidual sample of the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the residual blocks may be divided into one or moreentropy groups.

In the video encoding/decoding method and apparatus according to thepresent invention, the entropy group may be defined as a group ofresidual coefficients belonging to the same/similar frequency band.

In the video encoding/decoding method and apparatus according to thepresent invention, at least one of a scan order, an entropy decodingscheme, or a binarization scheme relating to one of a plurality ofentropy groups may be different from the other one of a plurality ofentropy groups.

In the video encoding/decoding method and apparatus according to thepresent invention, the number of entropy groups may be variablydetermined based on encoding information relating to the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the entropy group may be determined based on at leastone of the number of the residual coefficients belonging to the entropygroup or the scan order.

In the video encoding/decoding method and apparatus according to thepresent invention, the entropy group may be determined based on one, twoor more pieces of position information.

In the video encoding/decoding method and apparatus according to thepresent invention, the position information may indicate a position of aspecific residual coefficient belonging to the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the residual coefficients are derived throughscanning according to a predetermined scan order, and the scanning maybe performed for each entropy group.

In the video encoding/decoding method and apparatus according to thepresent invention, the scanning may be performed using a different scanorder for each entropy group.

In the video encoding/decoding method and apparatus according to thepresent invention, the scanning may be performed from a predeterminedstarting position within the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the starting position may be determined based on atleast one of information indicating a starting position of the scanningor information specifying an entropy group including a starting positionof the scanning.

In the video encoding/decoding method and apparatus according to thepresent invention, the step of deriving the residual coefficient mayfurther include setting a residual coefficient of a partial area in theresidual block to a default value pre-defined in the decoding apparatus.

In the video encoding/decoding method and apparatus according to thepresent invention, the partial area may be an area excluding at leastone of N columns from the left side or the M rows from the top side ofthe residual block, or may be an area excluding the N×M area in theresidual block.

In the video encoding/decoding method and apparatus according to thepresent invention, N and M may be derived based on information encodedto specify the partial area.

In the video encoding/decoding method and apparatus according to thepresent invention, the residual block may be a block divided into avariable size/shape based on at least one of a quadtree, a binary treeor a triple tree.

According to the present invention, encoding/decoding efficiency of aresidual block may be improved based on a predetermined entropy group.

According to the present invention, encoding/decoding efficiency of theresidual block may be improved by setting the residual coefficient of apredetermined area in the residual block to a pre-defined default value.

Also, according to the present invention, encoding/decoding efficiencymay be improved through block division of a tree structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an encoding apparatus accordingto an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a decoding apparatus according anexemplary embodiment of the present invention.

FIG. 3 illustrates a block division type according to an embodiment towhich the present invention is applied.

FIG. 4 illustrates a tree structure-based block division methodaccording to an embodiment in which the present invention is applied.

FIG. 5 illustrates a method of reconstructing a residual sampleaccording to an embodiment of the present invention.

FIG. 6 illustrates a method of deriving a quantization parameterprediction value (QPpred) according to an embodiment of the presentinvention.

FIG. 7 illustrates a method of deriving a quantization parameterprediction value for a chrominance component of a block T according toan embodiment of the present invention.

FIG. 8 illustrates a quantization parameter derivation method based on asignaling unit of a quantization parameter difference value (deltaQP)according to an embodiment of the present invention.

FIG. 9 illustrates an inverse transform process of a residualcoefficient according to an embodiment of the present invention.

FIG. 10 illustrates a shape of a scaling list related to a scalingprocess according to an embodiment of the present invention.

FIG. 11 illustrates a quantization weight-based scaling and inversetransform process according to an embodiment of the present invention.

FIGS. 12 and 13 illustrate a method of determining an entropy group of aresidual block according to an embodiment of the present invention.

FIG. 14 illustrates the relationship between scanning of residualcoefficients and a entropy group according to an embodiment of thepresent invention.

FIG. 15 illustrates a method of scanning a residual coefficientaccording to an embodiment of the present invention.

FIG. 16 illustrates a method of processing residual coefficients of apartial area in a residual block according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

A video encoding/decoding method and apparatus according to the presentinvention may derive a residual coefficient of a residual block,calculate a quantization parameter for the residual block, performdequantization on the residual coefficient using the calculatedquantization parameter for the residual block, and perform inversetransform on the dequantized residual coefficient to reconstruct aresidual sample of the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the residual blocks may be divided into one or moreentropy groups.

In the video encoding/decoding method and apparatus according to thepresent invention, the entropy group may be defined as a group ofresidual coefficients belonging to the same/similar frequency band.

In the video encoding/decoding method and apparatus according to thepresent invention, at least one of a scan order, an entropy decodingscheme, or a binarization scheme relating to one of a plurality ofentropy groups may be different from the other one of a plurality ofentropy groups.

In the video encoding/decoding method and apparatus according to thepresent invention, the number of entropy groups may be variablydetermined based on encoding information relating to the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the entropy group may be determined based on at leastone of the number of the residual coefficients belonging to the entropygroup or the scan order.

In the video encoding/decoding method and apparatus according to thepresent invention, the entropy group may be determined based on one, twoor more pieces of position information.

In the video encoding/decoding method and apparatus according to thepresent invention, the position information may indicate a position of aspecific residual coefficient belonging to the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the residual coefficients are derived throughscanning according to a predetermined scan order, and the scanning maybe performed for each entropy group.

In the video encoding/decoding method and apparatus according to thepresent invention, the scanning may be performed using a different scanorder for each entropy group.

In the video encoding/decoding method and apparatus according to thepresent invention, the scanning may be performed from a predeterminedstarting position within the residual block.

In the video encoding/decoding method and apparatus according to thepresent invention, the starting position may be determined based on atleast one of information indicating a starting position of the scanningor information specifying an entropy group including a starting positionof the scanning.

In the video encoding/decoding method and apparatus according to thepresent invention, the step of deriving the residual coefficient mayfurther include setting a residual coefficient of a partial area in theresidual block to a default value pre-defined in the decoding apparatus.

In the video encoding/decoding method and apparatus according to thepresent invention, the partial area may be an area excluding at leastone of N columns from the left side or the M rows from the top side ofthe residual block, or may be an area excluding the N×M area in theresidual block.

In the video encoding/decoding method and apparatus according to thepresent invention, N and M may be derived based on information encodedto specify the partial area.

In the video encoding/decoding method and apparatus according to thepresent invention, the residual block may be a block divided into avariable size/shape based on at least one of a quadtree, a binary treeor a triple tree.

The present invention may be changed and modified variously and beillustrated with reference to different exemplary embodiments, some ofwhich will be described and shown in the drawings. However, theseembodiments are not intended for limiting the invention but areconstrued as including includes all modifications, equivalents andreplacements which belong to the spirit and technical scope of theinvention. Like reference numerals in the drawings refer to likeelements throughout.

Although the terms first, second, etc. may be used to describe variouselements, these elements should not be limited by these terms. Theseterms are used only to distinguish one element from another element. Forexample, a first element could be termed a second element and a secondelement could be termed a first element likewise without departing fromthe teachings of the present invention. The term “and/or” includes anyand all combinations of a plurality of associated listed items.

It will be understood that when an element is referred to as being“connected to” or “coupled to” another element, the element can bedirectly connected or coupled to another element or interveningelements. On the contrary, when an element is referred to as being“directly connected to” or “directly coupled to” another element, thereare no intervening elements present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include” and/or“have,” when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the accompanying drawings. Like referencenumerals in the drawings refer to like elements throughout, andredundant descriptions of like elements will be omitted herein.

FIG. 1 is a block diagram illustrating an encoding apparatus accordingto an embodiment of the present invention.

Referring to FIG. 1, the encoding apparatus 100 includes a picturedividing unit 110, prediction units 120 and 125, a transform unit 130, aquantization unit 135, a reordering unit 160, an entropy encoding unit165, an inverse quantization unit 140, an inverse transform unit 145, afilter unit 150, and a memory 155.

Each of the elements shown in FIG. 1 is shown independently to representdifferent characteristic functions in the encoding apparatus, and maymean that each element is composed of separate hardware. But, theelements are independently arranged for convenience of description,wherein at least two elements may be combined into a single element, ora single element may be divided into a plurality of elements to performfunctions. It is to be noted that embodiments in which some elements areintegrated into one combined element and/or an element is divided intomultiple separate elements are included in the scope of the presentinvention without departing from the essence of the present invention.

Some elements are not essential to the substantial functions in theinvention and may be optional constituents for merely improvingperformance. The invention may be embodied by including onlyconstituents essential to embodiment of the invention, except forconstituents used to merely improve performance. The structure includingonly the essential constituents except for the optical constituents usedto merely improve performance belongs to the scope of the invention.

The picture dividing unit 110 may divide an input picture into at leastone block. At this time, a block may mean a coding unit (CU), aprediction unit (PU), or a transform unit (TU). The division may beperformed based on at least one of a quadtree, a binary tree, or atriple tree. The quadtree is a method of dividing an upper block intosub-blocks whose width and height are half of an upper block. The binarytree is a method of dividing an upper block into sub-blocks whose eitherwidth or height is half of an upper block. In a binary tree, a block mayhave a non-square shape as well as a square shape by dividing an upperblock based on the above-described binary tree-based division.

In the embodiments of the invention, a CU may be used to refer to notonly a unit of encoding but also a unit of decoding.

The prediction units 120 and 125 may include an inter prediction unit120 to perform inter prediction and an intra prediction unit 125 toperform intra prediction. The prediction units 120 and 125 may determinewhich of inter prediction and intra prediction is performed on a PU, andmay determine specific information (for example, an intra predictionmode, a motion vector, and a reference picture) of the determinedprediction method. Here, a processing unit on which prediction isperformed may be different from a processing unit for which a predictionmethod and specific information thereon are determined. For example, aprediction method and a prediction mode may be determined for each PU,while prediction may be performed for each TU. A residual value(residual block) between a generated predicted block and an originalblock may be input to the transform unit 130. Further, prediction modeinformation, motion vector information and the like used for predictionmay be encoded along with the residual value by the entropy encodingunit 165 and be transmitted to the decoding apparatus. When a specificencoding mode is used, the original block may be encoded and transmittedto the decoding apparatus without generating a prediction block by theprediction units 120 and 125.

The inter prediction unit 120 may predict a PU based on information onat least one picture among a previous picture of a current picture and asubsequent picture of a current picture. In some cases, the interprediction unit 120 may predict a PU based on information of a partiallyencoded region in the current picture. The inter prediction unit 120 mayinclude a reference picture interpolation unit, a motion predictionunit, and a motion compensation unit.

The reference picture interpolation unit may be supplied with referencepicture information from the memory 155 and generate pixel informationless than or equal to an integer pixel on a reference picture. In thecase of luminance pixels, a DCT-based 8-tap interpolation filter with avariable filter coefficient may be used to generate pixel informationless than or equal to an integer pixel in a unit of a ¼ pixel. In thecase of chrominance pixels, a DCT-based 4-tap interpolation filter witha variable filter coefficient may be used to generate pixel informationless than or equal to an integer pixel in a unit of a ⅛ pixel.

The motion prediction unit may perform motion prediction on the basis ofthe reference picture interpolated by the reference pictureinterpolation unit. Various methods, such as a full search-based blockmatching algorithm (FBMA), a three-step search (TSS) algorithm and a newthree-step search (NTS) algorithm, may be used to calculate a motionvector. A motion vector has a motion vector value in the unit of a ½ or¼ pixel on the basis of an interpolated pixel. The motion predictionunit may predict a current PU using different motion prediction methods.Various methods, such as skip mode, merge mode, and advanced motionvector prediction (AMVP) mode, etc. may be used as the motion predictionmethod.

The intra prediction unit 125 may generate a PU on the basis ofinformation on a reference pixel neighboring to a current block. When areference pixel is a pixel for which inter prediction has been performedbecause a block neighboring to the current PU is a block for which interprediction has been performed, information on a reference pixel in theblock for which inter prediction has been performed may be replaced withinformation on a reference pixel in a block for which intra predictionhas been performed. That is, when a reference pixel is not available,information on the unavailable reference pixel may be replaced withinformation on at least one reference pixel of the available referencepixels.

A prediction mode of intra prediction includes a directional predictionmode in which reference pixel information is used according to aprediction direction and a non-directional prediction mode in whichinformation on direction is not used in performing prediction. A modefor predicting a luminance component and a mode for predicting achrominance component may be different from each other. Further, achrominance component may be predicted by using either intra predictionmode used to obtain a luminance component or a predicted/reconstructedluminance component.

In the intra prediction method, a predicted block may be generated byapplying an adaptive intra smoothing (AIS) filter to the referencepixels according to the intra prediction mode. Different types of AISfilters may be applied to the reference pixels. In the intra predictionmethod, the intra prediction mode of a current PU may be predicted froman intra prediction mode of a PU neighboring to the current PU. Inpredicting the prediction mode of the current PU using mode informationpredicted from a neighboring PU, when the current PU and the neighboringPU have the same intra prediction mode, information indicating that thecurrent PU and the neighboring PU have the same intra prediction modemay be transmitted using predetermined flag information. When thecurrent PU and the neighboring PU have different intra prediction modes,information on the intra prediction mode of the current block may beencoded by entropy encoding.

A residual block including residual information may be generated. Theresidual information is a difference between an original block and apredicted block generated by the prediction units 120 and 125. Thegenerated residual block may be input to the transform unit 130.

The transform unit 130 may transform the residual block including theresidual data by using a transform type such as DCT, DST, or the like.At this time, the transform type may be determined based on the intraprediction mode of the prediction unit used to generate the residualblock.

The quantization unit 135 may quantize values transformed into afrequency domain by the transform unit 130. A quantization coefficientmay be changed depending on a block or importance of an image. Valuesoutput from the quantization unit 135 may be provided to the inversequantization unit 140 and the rearrangement unit 160.

The rearrangement unit 160 may perform the rearrangement of thecoefficient values on the quantized residual block.

The rearrangement unit 160 may change coefficients of a two-dimensional(2D) block into coefficients of a one-dimensional (1D) vector throughcoefficient scanning method. For example, the rearrangement unit 160 mayscan a DC coefficient to a coefficient in the high-frequency regionusing a predetermined scan type, and change it into a one-dimensionalvector form.

The entropy encoding unit 165 may perform entropy encoding on the basisof the values obtained by the rearrangement unit 160. Various encodingmethods, such as exponential Golomb coding, context-adaptive variablelength coding (CAVLC), or context-adaptive binary arithmetic coding(CABAC), may be used for entropy encoding.

The entropy encoding unit 165 may encode a variety of information, suchas residual coefficient information and block type information on a CU,prediction mode information, partitioning unit information, PUinformation, transfer unit information, motion vector information,reference frame information, block interpolation information andfiltering information from the rearrangement unit 160 and the predictionunits 120 and 125.

The entropy encoding unit 165 may entropy-encode coefficients of a CUinput from the rearrangement unit 160.

The inverse quantization unit 140 and the inverse transform unit 145dequantize the values which are quantized by the quantization unit 135and inverse-transform the values which are transformed by the transformunit 130. A reconstructed block may be generated by adding the residualvalues to the predicted PU. The residual values may be generated by theinverse quantization unit 140 and the inverse transform unit 145. Thepredicted PU may be predicted by the motion vector prediction unit, themotion compensation unit, and the intra prediction unit of theprediction units 120 and 125.

The filter unit 150 may include at least one of a deblocking filter, anoffset unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion generated byboundaries between blocks in a reconstructed picture. Whether to applythe deblocking filter to a current block may be determined on the basisof pixels included in several rows or columns of the block. When thedeblocking filter is applied to a block, a strong filter or a weakfilter may be applied depending on a required deblocking filteringstrength. When horizontal filtering and vertical filtering are performedin applying the deblocking filter, the horizontal filtering and verticalfiltering may be performed in parallel.

The offset unit may apply the offset with respect to the original imageto the deblocking filtered image, in units of pixels. A region to whichthe offset may be applied may be determined after partitioning pixels ofa picture into a predetermined number of regions. The offset may beapplied to the determined region in consideration of edge information oneach pixel or the method of applying the offset to the determinedregion.

The ALF may perform filtering based on a comparison result of thefiltered reconstructed image and the original image. Pixels included inan image may be partitioned into predetermined groups, a filter to beapplied to each group may be determined, and differential filtering maybe performed for each group. Information on whether to apply the ALF maybe transferred by each coding unit (CU) and a shape and filtercoefficients of an ALF to be applied to each block may vary. Further, anALF with the same form (fixed form) may be applied to a block regardlessof characteristics of the block.

The memory 155 may store a reconstructed block or picture output fromthe filter unit 150, and the stored reconstructed block or picture maybe supplied to the prediction units 120 and 125 when performing interprediction.

FIG. 2 is a block diagram illustrating a decoding apparatus according anexemplary embodiment of the present invention.

Referring to FIG. 2, the decoding apparatus 200 may include an entropydecoding unit 210, a rearrangement unit 215, a dequantization unit 220,an inverse transform unit 225, prediction units 230 and 235, a filterunit 240, and a memory 245.

Each of the elements shown in FIG. 2 is shown independently to representdifferent characteristic functions in the decoding apparatus, and maymean that each element is composed of separate hardware. But, theelements are independently arranged for convenience of description,wherein at least two elements may be combined into a single element, ora single element may be divided into a plurality of elements to performfunctions. It is to be noted that embodiments in which some elements areintegrated into one combined element and/or an element is divided intomultiple separate elements are included in the scope of the presentinvention without departing from the essence of the present invention.

The entropy decoding unit 210 may perform entropy decoding on the inputbitstream. For example, various methods, such as exponential Golombcoding, CAVLC or CABAC, may be used for entropy encoding.

The entropy decoding unit 210 may decode information associated withintra prediction and inter prediction performed by the encodingapparatus.

The rearrangement unit 215 may perform rearrangement on the bitstreamentropy-decoded by the entropy decoding unit 210. The rearrangement unit215 may reconstruct and rearrange coefficients of a 1D vector intocoefficients of a 2D block. The rearrangement unit 215 may be providedwith information on coefficient scanning performed by the encodingapparatus and may perform rearrangement using a method of inverselyscanning the coefficients, on the basis of scanning order performed bythe encoding apparatus.

The dequantization unit 220 may perform dequantization on the basis of aquantization parameter and the rearranged coefficients of the block.

The inverse transform unit 225 may perform inverse-transform of thedequantized transform coefficients based on a predetermined transformtype. At this time, the transform type may be determined based on atleast one of a prediction mode (inter/intra prediction), a size/shape ofa block, an intra prediction mode, a component type(luminance/chrominance component), or a partition type (QT, BT, TT,etc.)

The prediction units 230 and 235 may generate a prediction block on thebasis of information for generating prediction block and information ona previously-decoded block or picture provided. The information forgenerating prediction block may be provided from the entropy decodingunit 210. The information on a previously-decoded block or picture maybe provided from the memory 245.

The prediction units 230 and 235 may include a PU determination unit, aninter prediction unit and an intra prediction unit. The PU determinationunit may receive a variety of information, such as PU information, intraprediction mode-related information of the intra prediction method andmotion prediction-related information of an inter prediction method,etc. from the entropy decoding unit 210, may determine a PU for acurrent CU. The PU determination unit may determine which of the interprediction and the intra prediction is performed on the PU. An interprediction unit 230 may perform inter prediction on a current PU on thebasis of information on at least one picture among a previous pictureand a subsequent picture of a current picture including the current PU.An inter prediction unit 230 may use information necessary for interprediction for the current PU provided from the encoding apparatus. Theinter prediction may be performed on the basis of the information of thepre-reconstructed partial region in the current picture including thecurrent PU. To this end, the pre-reconstructed partial region may beadded to the reference picture list.

In order to perform inter prediction, it may be determined, in an unitof a CU, whether a motion prediction method for a PU included in the CUis a skip mode, a merge mode, an AMVP mode or a current picturereference mode.

An intra prediction unit 235 may generate a prediction block on thebasis of pixel information in a current picture. When a PU is a PU forwhich intra prediction is performed, intra prediction may be performedbased on intra prediction mode information on the PU provided from theencoding apparatus. The intra prediction unit 235 may include an AIS(Adaptive Intra Smoothing) filter, a reference pixel interpolation unit,and a DC filter. The AIS filter performs filtering on reference pixelsof a current block. The AIS filter may decide whether to apply thefilter or not, depending on a prediction mode for the current PU. AISfiltering may be performed on the reference pixels of the current blockusing the prediction mode for the PU and information on the AIS filterprovided from the encoding apparatus. When the prediction mode for thecurrent block is a mode not performing AIS filtering, the AIS filter maynot be applied.

When the prediction mode for the PU indicates a prediction mode ofperforming intra prediction on the basis of pixel values obtained byinterpolating the reference pixels, the reference pixel interpolationunit may generate reference pixels in a unit of a fractional pixel lessthan an integer pixel (i.e. full pixel) by interpolating the referencepixels. When the prediction mode for the current PU indicates aprediction mode of generating a prediction block without interpolatingthe reference pixels, the reference pixels may not be interpolated. TheDC filter may generate a prediction block through filtering when theprediction mode for the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit240. The filter unit 240 includes a deblocking filter, an offset unit,and an ALF.

The encoding apparatus may provide information on whether the deblockingfilter is applied to a corresponding block or picture, and informationon which of a strong filter and a weak filter is applied when thedeblocking filter is used. The deblocking filter of the decodingapparatus may be provided with information on the deblocking filter fromthe encoding apparatus and may perform deblocking filtering on acorresponding block.

The offset unit may apply offset to the reconstructed picture on thebasis of information on an offset type and offset value applied to thepicture in the encoding process.

The ALF may be applied to a CU on the basis of information on whetherthe ALF is applied and ALF coefficient information, etc. provided fromthe encoding apparatus. The ALF information may be included and providedin a specific parameter set.

The memory 245 may store the reconstructed picture or block for use as areference picture or a reference block and may provide the reconstructedpicture to an output unit.

FIG. 3 illustrates a block division type according to an embodiment towhich the present invention is applied.

One block (hereinafter, referred to as a first block) may be dividedinto a plurality of sub-blocks (hereinafter, referred to as a secondblock) by at least one of a vertical line or a horizontal line. Thenumber of each of the vertical and horizontal lines may be one, two, ormore. Here, the first block may be a coding block (CU) which is a basicunit of image encoding/decoding, a prediction block (PU) which is abasic unit of prediction encoding/decoding or a transform block (TU)which is a basic unit of transform encoding/decoding. The first blockmay be a square block or a non-square block.

The division of the first block may be performed based on a quad tree, abinary tree, a triple tree, etc., and will be described in detail withreference to FIG. 3.

FIG. 3(a) illustrates a quad tree division (QT). QT is a division typein which the first block is divided into four second blocks. Forexample, when the first block of 2N×2N is divided by QT, the first blockmay be divided into four second blocks having N×N size. QT may belimited to apply to a square block only, but it is also applicable to anon-square block.

FIG. 3(b) illustrates a horizontal binary tree (hereinafter, referred toas Horizontal BT) division. Horizontal BT is a division type in whichthe first block is divided into two second blocks by one horizontalline. This division may be performed symmetrically or asymmetrically.For example, when the first block of 2N×2N is divided based onHorizontal BT, the first block may be divided into two second blockswith a height ratio of (a:b). Here, a and b may be the same value, and amay be larger or smaller than b.

FIG. 3(c) illustrates a vertical binary tree (hereinafter, referred toas Vertical BT) division. Vertical BT is a division type in which thefirst block is divided into two second blocks by one vertical line. Thisdivision may be performed symmetrically or asymmetrically. For example,when the first block of 2N×2N is divided based on Vertical BT, the firstblock may be divided into two second blocks with a width ratio of (a:b).Here, a and b may be the same value, and a may be larger or smaller thanb.

FIG. 3(d) illustrates a horizontal triple tree (hereinafter, referred toas Horizontal TT) division. Horizontal TT is a division type in whichthe first block is divided into three second blocks by two horizontallines. For example, when the first block of 2N×2N is divided based onHorizontal TT, the first block may be divided into three second blockswith a height ratio of (a:b:c). Here, a, b, and c may be the same value.Alternatively, a and c may be the same, and b may be greater or lessthan a.

FIG. 3(e) illustrates a vertical triple tree (hereinafter, referred toas Vertical TT) division. Vertical TT is a division type in which thefirst block is divided into three second blocks by two vertical lines.For example, when the first block of 2N×2N is divided based on VerticalTT, the first block may be divided into three second blocks with a widthratio of (a:b:c). Here, a, b, and c may be the same value or differentvalues. Alternatively, a and c may be the same while b may be greater orless than a. Alternatively, a and b may be the same while c may begreater or less than a. Alternatively, b and c are the same while a maybe larger or smaller than b.

The division described above may be performed based on the divisioninformation signaled from the encoding apparatus. The divisioninformation may include at least one of division type information,division direction information, or division ratio information.

The division type information may specify any one of the division typesthat are pre-defined in the encoding/decoding apparatus. The pre-defineddivision type may include at least one of QT, Horizontal BT, VerticalBT, Horizontal TT, Vertical TT, or non-division mode (No split).Alternatively, the division type information may mean information onwhether or not QT, BT, or TT is applied, and may be encoded in the formof a flag or an index. In the case of BT or TT, the division directioninformation may indicate whether it is divided horizontally orvertically. In the case of BT or TT, the division ratio information mayindicate the ratio of the width and/or the height of the second block.

FIG. 4 illustrates a tree structure-based block division methodaccording to an embodiment in which the present invention is applied.

The block 400 illustrated in FIG. 4 is assumed to be a square block(hereinafter, referred to as a first block) having a size of 8N×8N and adivision depth k. When the division information of the first blockindicates QT division, the first block may be divided into foursub-blocks (hereinafter, referred to as a second block). The secondblock may have a size of 4N×4N and may have a division depth (k+1).

The four second blocks may be divided again based on either QT, BT, TT,or non-division mode. For example, when the division information of thesecond block indicates a horizontal binary tree (Horizontal BT), thesecond block is divided into two sub-blocks (hereinafter, referred to asa third block) as the second block 410 of FIG. 4. At this time, thethird block may have a size of 4N×2N and may have a division depth(k+2).

The third block may also be divided again based on either QT, BT, TT, ornon-division mode. For example, when the division information of thethird block indicates a vertical binary tree (Vertical BT), the thirdblock is divided into two sub-blocks 411 and 412 as illustrated in FIG.4. At this time, the sub-blocks 411 and 412 may have a size of 2N×2N anda division depth (k+3). Alternatively, when the division information ofthe third block indicates a horizontal binary tree (Horizontal BT), thethird block may be divided into two sub-blocks 413 and 414 asillustrated in FIG. 4. In this case, the sub-blocks 413 and 414 may havea size of 4N×N and a division depth (k+3).

The division may be performed independently or in parallel with theneighboring block, or may be performed sequentially according to apredetermined priority order.

The division information of the current block may be determineddepending on at least one of the division information of the upper blockof the current block or the division information of the neighboringblock. For example, when the second block is divided based on HorizontalBT and the upper third block is divided based on Vertical BT, the lowerthird block does not need to be divided based on Vertical BT. If thelower third block is divided by Vertical BT, this is the same result asthe second block is divided by QT. Therefore, encoding for the divisioninformation (particularly, the division direction information) of thelower third block may be skipped, and the decoding apparatus may be setso that the lower third block is divided in the horizontal direction.

The upper block may mean a block having a smaller division depth thanthe division depth of the current block. For example, when the divisiondepth of the current block is (k+2), the division depth of the upperblock may be (k+1). The neighboring block may be a block adjacent to thetop or left side of the current block. The neighboring block may be ablock having the same division depth as the current block.

The above-described division may be repeatedly performed up to theminimum unit of encoding/decoding. When divided into the minimum unit,the division information for the block is no longer signaled from theencoding apparatus. The information on the minimum unit may include atleast one of a size or a shape of the minimum unit. The size of theminimum unit may be expressed by the width, the height, the minimum ormaximum value of the width and height, the sum of the width and height,the number of pixels, or the division depth. The information on theminimum unit may be signaled in at least one of a video sequence, apicture, a slice, or a block unit. Alternatively, the information on theminimum unit may be a value pre-defined in the encoding/decodingapparatus. The information on the minimum unit may be signaled for eachof CU, PU, and TU. Information on one minimum unit may be applied to CU,PU, and TU equally.

FIG. 5 illustrates a method of reconstructing a residual sampleaccording to an embodiment of the present invention.

Referring to FIG. 5, the residual coefficient of the residual block maybe derived by entropy decoding the bitstream (S500).

The encoding apparatus may perform the transform and/or quantization onthe residual samples of the residual block to derive the residualcoefficients, and may encode the derived residual coefficients based ona predetermined encoding scheme. The encoding scheme may include atleast one of a scan order, an entropy encoding scheme, or a binarizationscheme. Examples of the entropy encoding scheme may include exponentialGolomb, CAVLC, CABAC, and the like. Examples of the binarization schememay include truncated Rice (TR) binarization, k-th order Exp-Colomb(EGk) binarization, fixed-length (FL) binarization, and the like.

At this time, the residual block may be divided into one or more groups(hereinafter, referred to as entropy groups), and each entropy group mayinclude at least one residual coefficient. The entropy group may mean agroup of residual coefficients having the same/similar frequency band.The frequency band may be divided into a low frequency band and a highfrequency band, or may be divided into three bands such as a lowfrequency band, an intermediate frequency band, and a high frequencyband. However, this is merely an example, and the frequency band may befurther subdivided considering the frequency property. The encoding ofthe residual coefficients may be performed for each entropy group in theresidual block.

The decoding apparatus may derive a residual coefficient from thebitstream based on a predetermined decoding scheme. The decoding schemeis based on the above-described encoding scheme, and a detaileddescription thereof will be omitted.

The decoding of the residual block may be performed for each entropygroup. For example, the entropy group to which the residual coefficientto be decoded belongs may be identified, and the residual coefficientmay be derived based on the decoding scheme corresponding to the entropygroup. At least one of the scan order, the entropy decoding scheme, orthe binarization scheme relating to one of a plurality of entropy groupsmay be different from the other one of a plurality of entropy groups.The entropy group-based residual coefficient derivation method will bedescribed with reference to FIGS. 12 to 15.

The derivation process of the residual coefficients may further includesetting a residual coefficient of a partial area (e.g., a high-frequencyarea) in the residual block to a default value pre-defined in thedecoding apparatus. This will be described with reference to FIG. 16.

Referring to FIG. 5, a quantization parameter for the residual block maybe calculated (S510).

The quantization parameter may be derived using at least one of aquantization parameter prediction value (QPpred) or a quantizationparameter difference value (deltaQP). In other words, the quantizationparameter may be set to be the quantization parameter prediction value(QPpred) or may be derived by adding the quantization parameterdifference value (deltaQP) to the quantization parameter predictionvalue (QPpred).

For example, when the dequantization is unnecessary for the block (e.g.,merge mode, skip mode, no-transform mode, PCM mode, a case that thereare no non-zero coefficients in the block (i.e., coded block flag=0),and the like), the quantization parameter difference value (deltaQP) maynot be encoded. In this case, the quantization parameter predictionvalue (Qppred) may be set equal to a quantization parameter.

A method of deriving the quantization parameter prediction value(QPpred) will be described with reference to FIGS. 6 and 7. Meanwhile,the quantization parameter difference value (deltaQP) may be signaled ina predetermined unit, and a quantization parameter deriving method basedon a signaling unit of the quantization parameter difference value(deltaQP) will be described with reference to FIG. 8.

The calculation of the quantization parameter may further include aprocess of modifying the derived quantization parameter based on thepredetermined quantization parameter offset (QPoffset).

The quantization parameter offset (QPoffset) may be a fixed value whichis pre-defined to the encoding/decoding apparatus, or may be encoded andsignaled by the encoding apparatus. The quantization parameter offset(QPoffset) may be signaled at at least one level of a video sequence,picture, slice, tile or block unit. The unit in which the quantizationparameter offset is signaled may be larger than the unit in which thequantization parameter difference value is signaled. The value and thenumber of the quantization parameter offset (Qpoffset) may be adaptivelydetermined according to a block size/shape, number of divisions, aprediction mode, an intra prediction mode, a component type (e.g.,luminance, chrominance), and the like.

The number of quantization parameter offsets may be one, two, three, ormore. For example, the quantization parameter offset may be defined inat least one of a picture level, a slice level, or a block level. Thequantization parameter offset may be defined for each of the intra modeand the inter mode, or may be defined for each of the luminancecomponent and the chrominance component. Alternatively, a separateoffset for the LM mode of the intra prediction mode may be defined.Here, the LM mode may mean a mode in which a chrominance block ispredicted using prediction/reconstruction samples of a luminance block.

Referring to FIG. 5, the dequantization may be performed on the residualcoefficient using the calculated quantization parameter (S520).

Specifically, the dequantization may be performed based on at least oneof the quantization parameter or a predetermined level scale value. Thelevel scale value may be a value pre-defined to the encoding/decodingapparatus, or may be encoded and signaled by the encoding apparatus. Thelevel scale value may be composed of k integer values of aone-dimensional array. For example, the level scale value may be definedas {40, 45, 51, 57, 64, 72}. However, this does not limit the number oflevel scale values and integer values. That is, the level scale valuemay be defined as another value, and the number of level scale valuesmay be defined as 4, 5, 7, 8, or more.

Meanwhile, a predetermined quantization weight m may be further appliedto the result of the dequantization, and this process is referred to asscaling. The scaling will be described with reference to FIGS. 10 and11.

Further, when the residual block includes a plurality of entropy groups,different quantization parameters may be applied for each entropy group.For example, each entropy group in the residual block shares the samequantization parameter difference value, but different quantizationparameter prediction values may be used. Conversely, each entropy groupof the residual block shares the same quantization parameter predictionvalue, but different quantization parameter difference values may beused. That is, the unit for calculating the quantization parameterprediction value may be different from the unit for calculating thequantization parameter difference value. In this case, thedequantization may be performed for each entropy group. Thedequantization process may be skipped for an entropy group having only aresidual coefficient of zero.

Referring to FIG. 5, a residual sample may be reconstructed byperforming an inverse transform on the dequantized residual coefficient(S530).

The inverse transform may be performed based on a predeterminedtransform type, and the transform type of the residual block may bedetermined based on the transform candidate set. The transform candidateset may include n transform types. For example, the transform candidateset may comprise at least one of DCT-II, DCT-V, DCT-VIII, DST-I orDST-VII.

In the encoding/decoding apparatus, m transform candidate sets may bedefined. Here, m may be 1, 2, 3 or more. The number and/or sort oftransform types belonging to one of the m transform candidate sets(hereinafter referred to as a first transform candidate set) may bedifferent from the other one (hereinafter referred to as a secondtransform candidate set). For example, the first transform candidate setmay be composed of p transform types, and the second transform candidateset may be composed of q transform types smaller than p. Alternatively,even when the first and second conversion candidate sets are composed ofthe same number of transform types, at least one transform typebelonging to the first conversion candidate set may be different fromthe transform type belonging to the second conversion candidate set.

Any one of the m transform candidate sets may be selectively used.

The selection of the transform candidate set may be performed based onthe size of the residual block. For example, if the size of the residualblock is less than or equal to the threshold value, the first transformcandidate set composed of p transform types is selected, and if not, thesecond transform candidate set composed of q transform types may beselected. The threshold value may be 32, 64, 128, 256 or more, and p maybe a value greater than q.

Alternatively, the selection of the transform candidate set may beperformed based on information to be signaled from the encodingapparatus. The information may specify any one of m transform candidatesets. The information may be signaled at at least one level of apicture, slice or block.

When the selected transform candidate set includes a plurality oftransform types, the encoding apparatus may encode informationspecifying any one of the plurality of transform types. The decodingapparatus may determine the transform type of the residual block bydecoding the encoded information.

Meanwhile, the inverse transform may be selectively performed based on apredetermined flag. Here, the flag may indicate whether the inversetransform is skipped for the residual block. For example, if the flag is1, an inverse transform is not performed on the residual block, and ifthe flag is 0, the inverse transform may be performed on the residualblock. Therefore, the transform type of the residual block may bederived only when the flag is 0. Alternatively, the inverse transformmay be selectively performed based on the properties of the residualblock. Based on the properties of the residual block, the decodingapparatus may determine whether or not the inverse transform is skipped.The properties may refer to the size/type of the residual block, thedivision type, the prediction mode, the component type, or otherresidual coefficient related encoding parameters.

Additional inverse transform (hereinafter referred to as a secondinverse transform) in addition to the inverse transform (hereinafterreferred to as a first inverse transform) may be performed, and thiswill be described with reference to FIG. 9.

FIG. 6 illustrates a method of deriving a quantization parameterprediction value (QPpred) according to an embodiment of the presentinvention.

Referring to FIG. 6, a quantization parameter prediction value (QPpred)for a block T may be derived based on a quantization parameter of aneighboring block. The block T is a block of an N×M size, and may besquare or non-square.

The neighboring block may be a block spatially/temporally adjacent tothe block T, and may be a block previously decoded before the block T.For example, the neighboring block may include at least one of a leftblock, a top block, a left-top block, a right-top block, or aleft-bottom block of the block T. Alternatively, the neighboring blockmay further include a collocated block which temporally corresponds tothe block T. The collocated block may be defined as a block belonging toa picture different from the block T and including a position of atleast one of a left-top corner sample, a bottom-right corner sample, ora center sample of the block T.

The position of the neighboring block may be a pre-defined position inthe encoding/decoding apparatus. For example, the pre-defined positionmay be a left block and a top block, or may be a left block, a topblock, and a top-left block. However, the present invention is notlimited to this, and may further include a bottom-left block, aright-top block, and the like. The position of the neighboring block maybe variably determined based on at least one property (e.g., size,shape, division depth, division type, component type, etc.) of at leastone of the block T or the neighboring block. For example, theneighboring block may be determined to be the block having the largestarea among the blocks adjacent to the block T, or may be determined tobe the block which the length of the boundary adjacent to each other isthe longest. This may be performed for the top block and the left blockof the block T, respectively.

Alternatively, the information specifying the position of theneighboring block may be encoded and signaled by the encoding apparatus.The information may be encoded in the form of a flag, an index, or thelike. For example, if the information is index 0, the quantizationparameter prediction value (QPpred) of block T may be derived using thequantization parameter of the left block. If the information is index 1,the quantization parameter prediction value (QPpred) of the block T maybe derived using the quantization parameter of the top block.

The number of the neighboring blocks is n, where n may be a naturalnumber of 1, 2, 3, 4, or more. The number may be a fixed valuepre-defined in the encoding/decoding apparatus. Alternatively, thenumber may be variably determined based on properties (e.g., size, type,division depth, division type, component type, etc.) of at least one ofthe block T or the neighboring block. Alternatively, the maximum numberinformation for the neighboring blocks used to derive the quantizationparameter prediction value (QPpred) of the block T may be encoded andsignaled by the encoding apparatus. That is, the block T may useneighboring blocks within the number range according to the maximumnumber information. The maximum number information may be signaled at alevel of at least one of a video sequence, a picture, and other fragmentarea (e.g., slice, tile, Coding Tree Block row, block).

As described above, the quantization parameter prediction value (QPpred)of block T may be derived using one or more neighboring blocks.

When a plurality of neighboring blocks are used, the quantizationparameter prediction value (QPpred) of the block T may be derivedthrough an operation process such as an intermediate value, an averagevalue, a minimum value, a maximum value, or a mode value of quantizationparameters of a plurality of neighboring blocks.

Alternatively, the quantization parameter predicted value (QPpred) ofthe block T may be derived by subtracting the QP of the top-left blockfrom the sum of the QP of the top block and the QP of the left block. Atthis time, if there are a plurality of top block or left block, the QPof the top block or the left block may be determined through anoperation process such as an intermediate value, an average value, aminimum value, a maximum value, or a mode value.

If there is an unavailable block among the neighboring blocks, thequantization parameter prediction value of the block T may be derivedusing only available neighboring blocks. Alternatively, when theneighboring block is unavailable, the quantization parameter of theneighboring block may be derived based on a quantization parameterdefined in a predetermined fragment area. The fragment area may be aslice, a tile, a Coding Tree Block row, a block, or the like. Thefragment area may denote an encoded/decoded area before the block T oran area to which the block T to be encoded/decoded belongs. Theunavailability may be a case where the neighboring block does not existphysically, or a case where reference is not possible according to therules of the encoding/decoding apparatus. For example, if block T and aneighboring block belong to different parallel processing areas (e.g.,slices, tiles, etc.), block T may not be allowed to refer to theneighboring block.

FIG. 7 illustrates a method of deriving a quantization parameterprediction value for a chrominance component of a block T according toan embodiment of the present invention.

Hereinafter, the luminance component and the chrominance component ofthe block T will be referred to as a luminance block and a chrominanceblock, respectively.

In case of 4:2:0 color format, the chrominance block T_(C) maycorrespond to the luminance block T_(Y). The quantization parameterprediction value of the chrominance block may be derived using thequantization parameter of the corresponding luminance block.

However, as illustrated in FIG. 7, the division structure between theluminance block and the chrominance block may be different. In thiscase, a chrominance block may correspond to a plurality of luminanceblocks. The quantization parameter prediction value of the chrominanceblock may be derived using a quantization parameter of one of theplurality of luminance blocks. At this time, a luminance blockcorresponding to the position of the center sample or the position ofthe top-left sample of the chrominance block may be used. A luminanceblock having the largest area overlapping the chrominance block may beused. Alternatively, the quantization parameter prediction value of thechrominance block may be derived through calculation of an averagevalue, a median value, a minimum value, a maximum value, a mode value,and the like of quantization parameters of a plurality of luminanceblocks.

The quantization parameter prediction value of the chrominance block maybe derived using the quantization parameter of the neighboring block,which has been described in detail with reference to FIG. 6, and adetailed description thereof will be omitted here.

As described above, the quantization parameter prediction value of thechrominance block may be derived by using both the method using thequantization parameter of the corresponding luminance block (firstmethod) and the method using the quantization parameter of theneighboring block of the chrominance block (second method).Alternatively, the quantization parameter prediction value of thechrominance block may be derived by selecting either the first method orthe second method.

The selection may be performed in consideration of whether or not theluminance block and the chrominance block have the same divisionstructure, the prediction mode, the intra prediction mode, the colorformat, or the size/shape relating to the block T. For example, if theblock T is encoded in the inter mode and the division structure of thechrominance block is the same as the division structure of the luminanceblock, the quantization parameter of the chrominance block may bepredicted using the first method. Alternatively, if the divisionstructure of the chrominance block is the same as the division structureof the luminance block, the first method is used; otherwise, the secondmethod may be used. Alternatively, if the intra prediction mode of theblock T is the LM mode, the quantization parameter of the chrominanceblock may be predicted using the first method.

Alternatively, the selection may be performed based on informationspecifying either the first method or the second method. The informationmay be encoded and signaled by an encoding apparatus. The informationmay be signaled at at least one level of a video sequence, picture, orother fragment area (e.g., slice, tile, Coding Tree Block row, andblock).

The quantization parameter of the chrominance block may be derived to bethe same as the derived quantization parameter prediction value of thechrominance block, or may be derived by adding a quantization parameterdifference value to the quantization parameter prediction value. Inaddition, the derived quantization parameter may be modified using apredetermined quantization parameter offset, as illustrated in FIG. 5.

For example, in the case of a chrominance block encoded in the LM mode,the quantization parameter prediction value may be set equal to aquantization parameter. In this case, the quantization parameterdifference value may not be signaled, or the process of adding thesignaled quantization parameter difference value may be omitted.Alternatively, in the case of a chrominance block encoded in the LMmode, the quantization parameter may be modified using one, two or morequantization parameter offsets.

FIG. 8 illustrates a quantization parameter derivation method based on asignaling unit of a quantization parameter difference value (deltaQP)according to an embodiment of the present invention.

The encoding apparatus may determine a unit of a block for encodingdeltaQP and encode information indicating the size of the block. Here,the size may be represented by at least one of a width or a height of ablock, a product of a width and a height, a sum of a width and a height,and a minimum value/a maximum value of a width and a height.

The decoding apparatus decodes the signaling information to obtain theminimum size of a block in which signaling of deltaQP is allowed. Theinformation may be signaled at a level of at least one of a videosequence, a picture, a slice, or a tile. Alternatively, the minimum sizemay be derived as a minimum size of the transform block, or may bedefined as a fixed size pre-defined in the encoding/decoding apparatus.

For example, the minimum size may be defined as 4×4, 8×4, 4×8, 8×8, andthe like. The information indicating the size of the block may besignaled for the luminance component and the chrominance component,respectively. Alternatively, the minimum size for the chrominance blockmay be derived based on the minimum size for the luminance block.

For example, in 4:2:0 color format, the minimum size of the chrominanceblock may be determined to be half of the minimum size of the luminanceblock. In the inter mode, the division structure of the chrominanceblock may be different from that of the luminance block, and the minimumsize of the chrominance block may be determined to be half of theluminance block.

Referring to FIG. 8, the quantization parameter of the current block maybe derived based on the comparison result between the size of thecurrent block and the minimum size. Here, the current block may be ablock that is not further divided by the block division type such as QT,BT, TT, or the like.

FIG. 8(a) illustrates a case where the size of the current block is2M×2N and the minimum size is M×N. As illustrated in FIG. 8(a), when thesize of the current block is larger than the minimum size, thequantization parameter of the current block may be derived using QPpredand signaled deltaQP.

The QPpred may be derived based on at least one of the first method orthe second method described above. The deltaQP may be signaled at blocka and the remaining blocks b, c, d may share the deltaQP signaled fromblock a. In this case, the current block has one quantization parameter.Alternatively, the deltaQP may be signaled for each of blocks a-d withthe minimum size. In this case, a quantization parameter may be derivedfor each of the blocks a-d belonging to the current block, and blocksa-d may have different quantization parameters.

Meanwhile, if the size of a current block is equal to the minimum size,it may be derived using the QPpred and the signaled deltaQP.

FIG. 8(b) illustrates a case where the minimum size is M×N and thecurrent block (a-d) is smaller than the minimum size. As illustrated inFIG. 8(b), if the size of the current block is smaller than the minimumsize, the quantization parameter of the current block may be derivedusing QPpred and signaled deltaQP.

The QPpred may be derived, based on the current block, using at leastone of the first method or the second method described above. Forexample, QPpred may be derived for each of blocks a-d. Alternatively,QPpred may be derived for block a, and the remaining blocks b-d mayshare QPpred derived from block a.

Alternatively, the QPpred may be derived, based on the upper block ofthe current block, using at least one of the first method or the secondmethod described above. Here, the upper block may be a block includingthe current block and a block having a smaller depth than the currentblock. For example, when the division depth of the current block is k,the division depth of the upper block may be (k−1), (k−2), and so on.The upper block may be defined as a unit of a block sharing the QPpred.The upper block may be set to a size (M×N) equal to the minimum size.

Alternatively, the encoding apparatus may determine a unit of a blocksharing the QPpred, and may encode information specifying a unit of theblock. The decoding apparatus may specify the position, size, shape andthe like of the upper block based on the encoded information.

The deltaQP may be signaled in the upper block of the current block.Here, the upper block may be a block including a current block, and ablock having a smaller depth than the current block. That is, when thedivision depth of the current block is k, the division depth of theupper block may be (k−1), (k−2), and so on. Here, it is assumed that theupper block is M×N illustrated in FIG. 8(b). Thus, a single and samequantization parameter may be derived for blocks a-d, and a differentquantization parameter may be derived for each of blocks a-d.Alternatively, if the size of the current block is smaller than theminimum size as illustrated in FIG. 8(b), the quantization parameter ofthe current block may be derived using QPpred. At this time, decodingfor deltaQP may be omitted.

As described above, the QPpred may be derived, based on the currentblock or the upper block, using at least one of the first method and thesecond method, and a detailed description thereof will be omitted.Similarly, a single and same quantization parameter may be derived forthe blocks a-d belonging to the M×N block, and a different quantizationparameter may be derived for each of blocks a-d.

On the other hand, in the case of a block adjacent to the boundary of apicture, a slice, or a tile, the block may not satisfy the minimum size.In this case, the quantization parameter of the block may be derivedusing only QPpred, and decoding for deltaQP may be omitted.

FIG. 9 illustrates an inverse transform process of a residualcoefficient according to an embodiment of the present invention.

Referring to FIG. 9, a residual sample of a residual block may bereconstructed by performing at least one of a first inverse transform ora second inverse transform on the residual coefficient.

The second inverse transform may be applied to the entire area of theresidual block or a partial area within the residual block. The partialarea may mean a low frequency area in the residual block. The area towhich the second inverse transform is applied may be variably determinedin consideration of at least one of the size/shape of the residual blockor the size/shape of the transform matrix of the second inversetransform.

For example, if either the width or the height of the residual block isequal to or greater than 8, a second inverse transform with an 8×8transform matrix may be applied. When the size of the residual block is8×8, the second inverse transform is applied to the entire area of theresidual block, and when the size of the residual block is 16×16, thesecond inverse transform may be applied to only a partial area of theresidual block. The partial area may be an 8×8 area located at thetop-left of the residual block, a 16×8 area located at the top end ofthe residual block, an 8×16 area located at the left of the residualblock, or the area excluding the 8×8 area located at the bottom-right ofthe residual block.

Alternatively, if either the width or height of the residual block is 4,a second inverse transform with a 4×4 transform matrix may be applied.When the size of the residual block is 4×8 or 8×4, the second inversetransform may be applied only to a partial area of the residual block(e.g., a 4×4 area located at the top-left of the residual block), andthe second inverse transform may be applied to each of two 4×4 areasbelonging to the residual block.

The size of the transform matrix of the second inverse transform may be4×4, 8×8, 16×16, 32×32 or more. The shape of the transform matrix is notlimited to a square, but may be implemented as a non-square. However, inorder to reduce the complexity of the transform, the size of thetransform matrix allowed for the second inverse transform may be limitedto N×M or less. N and M may be 4, 8, or 16, respectively, and N and Mmay be the same or different from each other.

In the second inverse transform process, the transform type of theresidual block may be determined through the transform type derivationmethod described in FIG. 5. Alternatively, the transform type in thesecond inverse transform may be pre-defined in the encoding/decodingapparatus. For example, as the transform type in the second inversetransform, one of the above-mentioned five transform types may befixedly used.

The second inverse transform may be selectively performed based on aflag indicating whether or not the first inverse transform is skipped(hereinafter referred to as a first flag) in the residual block. Thatis, when the first inverse transform is skipped in the residual blockaccording to the first flag, the performance of the second inversetransform may be skipped.

Alternatively, a flag indicating whether or not the second inversetransform is skipped (hereinafter referred to as a second flag) may besignaled separately. If the second flag is 1, a second inverse transformis not performed, and if the flag is 0, a second inverse transform maybe performed.

The first flag and the second flag may be independently encoded andsignaled. Alternatively, either one of the first flag and the secondflag may be signaled depending on the other. For example, only wheneither one of the first flag and the second flag is 1, the other may besignaled. Conversely, only when either one of the first flag and thesecond flag is 0, the other may be signaled.

The second inverse transform may not be applied when the number ofnon-zero residual coefficients belonging to the residual block issmaller than n. Where n may be a value pre-defined to theencoding/decoding apparatus. For example, n may be a natural number of1, 2, 3 or 8 or less. Alternatively, n may be variably determined basedon the size of the residual block.

Meanwhile, FIG. 9 illustrates performing the second inverse transformbefore the first inverse transform, but it does not limit the order ofperforming the inverse transform. That is, the second inverse transformmay be performed before the first inverse transform, or may be performedafter the first inverse transform. When the second inverse transform isperformed before the first inverse transform, the scaling described inFIG. 5 may be performed between the dequantization and the secondinverse transform, or may be performed between the first inversetransform and the second inverse transform. Conversely, when the secondinverse transform is performed after the first inverse transform, thescaling described in FIG. 5 may be performed between the dequantizationand the first inverse transform, or may be performed between the firstinverse transform and the second inverse transform.

FIG. 10 illustrates a shape of a scaling list related to a scalingprocess according to an embodiment of the present invention.

As mentioned in FIG. 5, the scaling may refer to a process of applying apredetermined quantization weight (m) to a residual coefficient of aresidual block. The residual coefficient of the residual block may besquare or N×M non-square. The quantization weight may be defined foreach frequency in the residual block, and an array of quantizationweights defined for each frequency will be referred to as a scalinglist.

The quantization weight of the scaling list may be signaled at theencoding apparatus (Method A).

With respect to Method A, the quantization weight may be signaled foreach of the positions or frequency components of the residualcoefficients in the residual block. The quantization weight may besignaled at at least one level of a video sequence, a picture, or otherfragment area (e.g., slice, tile, Coding Tree Block row, and block).

As illustrated in FIG. 10, a scaling list having various sizes/shapesdetermined by the combination of N and M may be signaled. Here, N and Mmay be integers greater than or equal to 1. The scaling list may besignaled in a two-dimensional form of N×M, or may be signaled byarranging a two-dimensional array of N×M in one dimension.Alternatively, the scaling list may be signaled by dividing into ahorizontal scaling list of N×1 and a vertical scaling list of 1×M.

The shape of the scaling list may differ depending on whether thescaling is performed before the second inverse transform according toFIG. 9. For example, when the scaling is performed before the secondinverse transform, it is signaled in one-dimensional form, otherwise itmay be signaled in two-dimensional form.

The quantization weight of the scaling list may be a value pre-set inthe encoding/decoding apparatus (Method B). With respect to Method B,the quantization weight may be one and the same value regardless of theposition of the residual coefficients in the residual block.Alternatively, the quantization weight may be derived based on the tableinformation that is pre-defined in the encoding/decoding apparatus. Thetable information may define a quantization weight according to at leastone of a position of a residual coefficient, a block size, a componenttype, and a prediction mode.

The quantization weight of the scaling list may be determined byreferring to all or part of a previously used or signaled scaling list(Method C). The scaling list to be referred to may be the most recentlyused or signaled in the encoding/decoding order, or may be used orsignaled in a previous fragment area (eg, a slice, a tile, a Coding TreeBlock (CTB) row, a CTB, other sub-block). To this end, informationindicating whether to refer to a previous scaling list may be encodedand signaled. Information specifying the quantization weight reused inthe previous scaling list may be encoded and signaled.

The quantization weight may be determined by selectively using one ofMethods A to C described above. The selection may be performed based onat least one of the size/type of the residual block, the division type,the prediction mode, the component type, the transform type, orpredetermined flag information. The flag information may include a flagrelated to whether or not a quantization weight is applied, a flagrelated to whether or not to perform a transform skip, and the like.

In Methods A to C described above, the quantization weight of thescaling list may be determined for each of the luminance block and thechrominance block. For example, if the color format is 4:2:0 or 4:2:2, ascaling list for each of the luminance block and the chrominance blockmay be signaled. Alternatively, the scaling list of the chrominanceblock may be determined by sampling the scaling list of the luminanceblock at a predetermined ratio. The ratio may be determined based on acolor format which is a ratio between a luminance component and achrominance component.

Alternatively, in the above-described Methods A to C, the scaling listmay be determined differently depending on the transform type of theresidual block. The transform type of the residual block may bedetermined for the vertical transform and the horizontal transform,respectively. The scaling list may be determined differently dependingon the determined transform type of the vertical/horizontal transform.The transform type of the residual block may be determined in at leastone of the first inverse transform or the second inverse transformaccording to FIG. 9.

FIG. 11 illustrates a quantization weight-based scaling and inversetransform process according to an embodiment of the present invention.

At least one of a quantization weight-based scaling or inverse transformmay be performed by dividing into the horizontal direction and thevertical direction.

As mentioned in FIG. 10, the scaling list may be signaled by dividinginto a horizontal scaling list of N×1 and a vertical scaling list of1×M. In this case, the decoding apparatus may perform each of ahorizontal scaling based on the horizontal scaling list (hereinafter,referred to as 1D horizontal scaling) and a vertical scaling based onthe vertical scaling list (hereinafter referred to as 1D verticalscaling). And, the inverse transform may be performed on the residualcoefficients to which the scaling is applied. In this case, thehorizontal transform (hereinafter, referred to as 1D horizontaltransform) may be performed on the residual coefficients to which the 1Dhorizontal scaling is applied. And, the vertical transform (hereinafter,referred to as 1D vertical transform) may be performed on the residualcoefficients to which the 1D vertical scaling is applied. Alternatively,horizontal and vertical transforms (hereinafter referred to as 2Dinverse transform) may be performed on the residual coefficients towhich the scaling is applied.

For example, as illustrated in FIG. 11, the scaling and inversetransform for the residual coefficients may include performing 1Dhorizontal (vertical) transform after 1D horizontal (vertical) scaling(hereinafter referred to as a first step) and performing 1D vertical(horizontal) transform after 1D vertical (horizontal) scaling(hereinafter referred to as a second step). The scaling and inversetransform may be sequentially performed in the order of the first stepto the second step, and the first step and the second step may beperformed in parallel.

Alternatively, the horizontal/vertical transform may be performed afterthe horizontal/vertical scaling with respect to the residualcoefficients. That is, scaling and inverse transform of the residualcoefficients may be performed in the order of 1D horizontal (vertical)scaling→1D vertical (horizontal) scaling→1D horizontal (vertical)transform→1D vertical (horizontal) transform. The 1D horizontal(vertical) scaling and 1D vertical (horizontal) scaling may be performedsequentially or in parallel. Likewise, 1D horizontal (vertical)transform and 1D vertical (horizontal) transform may be performedsequentially or in parallel.

On the other hand, the scaling list may be signaled in a two-dimensionalform of N×M. In this case, the scaling list-based scaling (hereinafter,referred to as 2D scaling) may be performed and the inverse transformmay be performed on the scaled residual coefficients. Alternatively, thescaling list may be signaled in the form of a one-dimensional array ofN×M two-dimensional arrays, or may be signaled by dividing into ahorizontal scaling list of N×1 and a vertical scaling list of 1×M. Inthis case, the decoding apparatus may rearrange the signaled scalinglist into two dimensions of N×M. The decoding apparatus may performinverse transform after 2D scaling on the residual coefficients. Here,the inverse transform may be performed by dividing into 1D horizontaltransform and 1D vertical transform, or may be 2D inverse transform.

When the scaling is performed before the second inverse transformaccording to FIG. 9, the inverse transform in this embodiment may meanthe second inverse transform. On the other hand, when the scaling isperformed between the first inverse transform and the second inversetransform according to FIG. 9, the inverse transform in this embodimentmay mean the first inverse transform.

FIGS. 12 and 13 illustrate a method of determining an entropy group of aresidual block according to an embodiment of the present invention.

The number of entropy groups belonging to the residual block may be n.For example, the residual block may be divided into two entropy groups:a first group which is a low frequency region and a second group whichis a high frequency region. Alternatively, the residual block may bedivided into three entropy groups: a first group which is a lowfrequency region, a second group which is a middle frequency region, anda third group which is a high frequency region. However, this is merelyan example, and n may be 1, or may be an integer greater than or equalto 4.

The value n may be a value pre-defined in the encoding/decodingapparatus, or may be derived based on information signaled from theencoding apparatus. The information may include information indicatingwhether the residual block is divided into a plurality of entropygroups, information indicating the number of entropy groups belonging tothe residual block, and the like. The information may be signaled at atleast one level of a video sequence, picture, or other fragment area(e.g., slice, tile, Coding Tree Block row, coding block, transformblock).

Alternatively, the value n may be variably determined based on theencoding information about the residual block. The encoding informationmay include not only information encoded and signaled by the encodingapparatus but also information derived in the decoding apparatus basedon the signaled information.

For example, the encoding information may include at least one of ablock size/shape, a block availability, a division type, number ofdivisions, a component type, a prediction mode, information on an intraprediction mode, an inter mode, motion information, a transform type, atransform skip mode, information about non-zero residual coefficients,scan order, color format, in-loop filter information, and the like.

The block size may be expressed by one of a width and a height, aminimum value/maximum value of a width and a height, a sum of a widthand a height, the number of samples belonging to a block, and the like.The availability of the block may be determined in consideration of theblock position, the range of the parallel processing area, the decodingorder, and the like. The prediction mode may mean information indicatingan intra mode or an inter mode. The information on the intra predictionmode includes information relating to whether the intra prediction modeis the non-directional mode, whether the intra prediction mode is thevertical/horizontal mode, the directionality of the intra predictionmode, the number of intra prediction modes pre-defined in theencoding/decoding apparatus, and the like. The inter mode may meaninformation indicating a merge/skip mode, an AMVP mode, or a currentpicture reference mode. The current picture reference mode refers to amethod of predicting a current block using the pre-reconstructed area ofthe current picture. The current picture may be a picture to which thecurrent block belongs. The current picture may be added to a referencepicture list for inter prediction, and the current picture may bearranged, in a reference picture list, after a short-term referencepicture or a long-term reference picture. The motion information mayinclude a prediction direction flag, a motion vector, a referencepicture index, and the like. The encoding information may be related toat least one of a current block, a neighboring block of a current block,or an upper block of a current block. The upper block may mean a blockhaving a smaller division depth than the current block.

Referring to FIG. 12, the entropy group may be determined based on atleast one of the number of residual coefficients belonging to theentropy group (hereinafter referred to as coefficient numberinformation) or the scanning order. The coefficient number informationmay be defined for each entropy group.

For example, it is assumed that coefficient number information of thefirst group and the second group indicates 3 and 7, respectively, andthat the scanning order is a zigzag scan. In this case, as illustratedin FIG. 12, according to the zigzag scan, the first group is determinedas a group of three residual coefficients (that is, a group of residualcoefficients at positions 0 to 2) and the second group is determined asa group of seven residual coefficients (that is, a group of residualcoefficients at positions 3 to 9), and the third group may be determinedas a group of residual coefficients excluding the first group and thesecond group in the residual block.

As described above, the first group is defined as a group from thetop-left residual coefficient of the residual block to the residualcoefficient C1 at the position shifted by the coefficient numberinformation of the first group. Similarly, the second group is definedas a group from the residual coefficient C1 to the residual coefficientC2 at a position shifted by the coefficient number information of thesecond group. The third group is defined as a set of residualcoefficients excluding the first group and the second group in theresidual block. The shifting is in accordance with the (inverse) scanorder of the residual block or each group.

The coefficient number information may be a value pre-defined in theencoding/decoding apparatus (first embodiment). Alternatively, thecoefficient number information may be signaled at at least one level ofa video sequence, a picture, and other fragment area (eg, a slice, atile, a coding tree block row, a coding block, a transform block)(second embodiment). Alternatively, the coefficient number informationmay be variably determined based on the encoding information about theresidual block (third embodiment). Here, the encoding information is thesame as the above-described encoding information, and a detaileddescription thereof will be omitted. The coefficient number informationmay be derived based on coefficient number information of apredetermined reference block (fourth embodiment). Here, the referenceblock may be a neighboring block or an upper block of the residualblock. The neighboring block refers to a pre-decoded block before theresidual block, and may be at least one of blocks adjacent to aleft/right or a top/bottom of the residual block. The upper block may bea block having a smaller division depth than the residual block.

On the other hand, the coefficient number information of some groupsamong a plurality of entropy groups may be determined based on one ofthe first to fourth embodiments described above, and the coefficientnumber information of some other groups may be determined based on theother one of the first to fourth embodiments described above.

One entropy group may be determined based on one, two or more pieces ofposition information. The position information may indicate the positionof a specific residual coefficient belonging to the residual block, andmay be information for specifying the size, shape, position, etc. of theentropy group.

Referring to FIG. 13(a), the entropy group may be distinguished based onthe position information of one residual coefficient. In this case, whenthe number of entropy groups belonging to the residual block is n, thenumber of position information may be (n−1).

For example, when the position information of the first group specifiesthe position (X_(A), Y_(A)) of the residual coefficient A, the firstgroup may be determined as a group of residual coefficients at theposition (x1, y1) (where, 0=<x1=<X_(A), 0=<y1=<Y_(A)). When the positioninformation of the second group specifies the position (X_(B), Y_(B)) ofthe residual coefficient B, the second group may be determined as agroup excluding the first group in residual coefficients at position(x2, y2) (where, 0=<x2=<X_(B), 0=<y2=<Y_(B)). The third group may bedetermined as a group of residual coefficients excluding the first groupand the second group in the residual block.

Referring to FIG. 13(b), the entropy group may be distinguished based ona plurality of pieces of position information.

For example, when the position information of the first group specifiesthe positions of the residual coefficients A1 and A2, the first groupmay be determined as a group of residual coefficients located on theleft side of the line passing through A1 and A2. That is, the firstgroup may be composed of 10 residual coefficients. When the positioninformation of the second group specifies the position of the residualcoefficients B1 and B2, the second group may be determined as a groupexcluding the first group in a group of residual coefficients located onthe left side of the line passing through B1 and B2. That is, the secondgroup may be composed of 26 residual coefficients. The third group maybe determined as a group of residual coefficients excluding the firstgroup and the second group in the residual block.

The first group may be determined using two pieces of positioninformation specifying positions of A1 and A2, respectively and thesecond group may be determined using two pieces of position informationspecifying positions of B1 and B2, respectively have. However, asillustrated in FIG. 13(b), the entropy group may be implemented in asymmetrical form, based on the diagonal line L of the residual block. Inthis case, any one of the two pieces of position information may bederived based on the other. For example, the position information of A2may be derived based on the position information of A1. Similarly, theposition information of B2 may be derived based on the positioninformation of B1.

Further, some of the plurality of entropy groups may be determined basedon one piece of position information, and the rest may be determinedbased on two or more pieces of position information. For example, thefirst group is determined based on one piece of position information asin the embodiment of FIG. 13(a), and the second group is determinedbased on two piece of position information as in the embodiment of FIG.13(b). Conversely, the first group is determined based on two pieces ofposition information as in the embodiment of FIG. 13(b), and the secondgroup is determined based on one piece of position information as in theembodiment of FIG. 13(a).

The position information may be a value pre-defined in theencoding/decoding apparatus (first embodiment). Alternatively, theposition information may be signaled at at least one level of a videosequence, picture, other fragment area (eg, slice, tile, Coding TreeBlock row, coding block, transform block) (second embodiment). At thistime, the block level may be a unit with a fixed size such as 4×4, 8×8,or 16×16. However, this does not limit the shape of the block level, andthe block level may be a non-square unit with a fixed size.Alternatively, the position information may be variably determined basedon the encoding information about the residual block (third embodiment).Here, the encoding information is the same as the above-describedencoding information, and a detailed description thereof will beomitted. Alternatively, the position information may be derived based onposition information in a predetermined reference block (fourthembodiment). Here, the reference block is the same as theabove-described reference block, and a detailed description will beomitted.

On the other hand, the position information of some groups of theplurality of entropy groups may be determined based on one of the firstto fourth embodiments, and the position information of the other groupsmay be determined based on the other one of the first to fourthembodiments.

FIG. 14 illustrates the relationship between scanning of residualcoefficients and a entropy group according to an embodiment of thepresent invention.

The decoding apparatus may derive the residual coefficient of theresidual block through scanning according to a predetermined scan order.The scan order includes zigzag scan, z scan, up-right diagonal scan,bottom-left diagonal scan, horizontal scan, and vertical scan. Here, theup-right diagonal scan may mean a diagonal scan from the top-right endto the bottom-left end of the residual block, and the bottom-leftdiagonal scan may mean a diagonal scan from the bottom-left end to thetop-right end of the residual block.

When the residual block includes a plurality of entropy groups, the scanmay be performed regardless of the entropy group, or may be performedfor each entropy group. The residual block may use only one scan orderfor the scanning, or may use a different scan order for each entropygroup.

Specifically, referring to FIG. 14(a), the residual block may includethree entropy groups. The three entropy groups belonging to the residualblock may use one and the same scan order, i.e., a zigzag scan. However,the scanning based on the zigzag scan is not performed in a unit of aentropy group, but may be performed in a unit of a residual block.Therefore, at least one of the residual coefficients of the firstentropy group located at the top-left of the residual block may bescanned earlier than at least one of the residual coefficients of thesecond entropy group.

On the other hand, referring to FIG. 14(b), the residual block mayinclude two entropy groups. Scanning for residual coefficients may beperformed in a unit of a entropy group, respectively. At this time, thescan order of the first entropy group may be different from the scanorder of the second entropy group. For example, the scan order of thefirst entropy group may be a zigzag scan, and the scan order of thesecond entropy group may be a vertical scan. Scanning for residualcoefficients may be performed from the bottom-right to the top-left ofthe residual block. The scanning for the first entropy group may beperformed after the scanning is completed for all the residualcoefficients of the second entropy group.

Referring to FIG. 14(c), the residual block may include two entropygroups. Scanning for residual coefficients may be performed in a unit ofa entropy group, respectively. At this time, the scan order of the firstentropy group may be the same as the scan order of the second entropygroup. For example, the scan order of both the first and second entropygroups may be a vertical scan. Scanning for residual coefficients may beperformed from the bottom-right to the top-left of the residual block.The scanning for the first entropy group may be performed after thescanning is completed for all the residual coefficients of the secondentropy group.

Hereinafter, a method for determining the scan order of the residualblocks will be described. As described above, in a unit of a residualblock, one or more scan orders may be used. At this time, at least oneof zigzag scan, z scan, up-right diagonal scan, bottom-left diagonalscan, horizontal scan, and vertical scan may be selectively used.

The scan order may be set to be a default mode pre-defined in theencoding/decoding apparatus (first embodiment). For example, thepre-defined default mode may be a zig-zag scan or a z-scan. The scanorder may be derived based on information signaled from the encodingapparatus (second embodiment). The information may mean informationspecifying the scan order of the residual block. The information may besignaled at at least one level of a video sequence, picture, and otherfragment area (e.g., slice, tile, Coding Tree Block row, coding block,transform block). The information may be signaled for each entropygroup, or may be signaled in a unit of a residual block.

Alternatively, the scan order may be determined based on the encodinginformation about the residual block (third embodiment). The encodinginformation may include not only information encoded and signaled by theencoding apparatus but also information derived in the decodingapparatus, based on the signaled information. For example, the encodinginformation may include at least one of a block size/type, a blockavailability, a division type, number of divisions, a component type, aprediction mode, information on an intra prediction mode, an inter mode,motion information, a transform type, a transform skip mode, informationabout non-zero residual coefficients, color format, size/shape ofentropy group, and the like. This is as described with reference to FIG.12, and a detailed description will be omitted.

Alternatively, the scan order may be derived based on a scan order of apredetermined reference block (fourth embodiment). Here, the referenceblock may be a neighboring block or an upper block of the residualblock. The neighboring block refers to a pre-decoded block before theresidual block, and may be at least one of blocks adjacent to aleft/right or an top/bottom end of the residual block. The upper blockmay be a block having a smaller division depth than the residual block.

On the other hand, when one residual block uses a plurality of scanorders, one part of the plurality of scan orders is determined based onone of the first to fourth embodiments described above, and the otherpart is determined based on the other one of the first to fourthembodiments.

FIG. 15 illustrates a method of scanning a residual coefficientaccording to an embodiment of the present invention.

Scanning may be performed from the starting position of scanning in theresidual block. The starting position may indicate the position of thespecific residual coefficient of the residual block. The specificresidual coefficient may mean a residual coefficient having a non-zerointeger value (hereinafter referred to as a non-zero value). Thespecific residual coefficient may be located at the end of the non-zerovalues belonging to the residual block in the inverse scan order.Conversely, the specific residual coefficient may be located at thebeginning of the non-zero values belonging to the residual block in thescan order.

For example, the scanning may be performed based on informationindicating a starting position of scanning (hereinafter referred to asfirst information). The first information may be encoded and signaled byan encoding apparatus. Scanning may be performed from a positionspecified by the first information. As illustrated in FIG. 15(a), thestarting position of the scanning may be specified as the A positioninstead of the bottom-right position of the residual block, based on thefirst information. In this case, the residual coefficient existingbetween the A position and the bottom-right position of the residualblock in the scan order may be set equal to zero. The residualcoefficient at the bottom-right position of the residual block may alsobe set equal to zero.

Alternatively, the scanning may be performed based on informationspecifying an entropy group including a starting position of scanning(hereinafter referred to as second information). The second informationmay be encoded and signaled by an encoding apparatus. Based on thesecond information, an entropy group including a starting position ofscanning is specified, and scanning may be performed from the specifiedentropy group. At this time, the scan order between the entropy groupsdepends on the scan order for the residual coefficients. According tothe second information, scanning may be skipped for some entropy groupof the residual block. The residual coefficient of the entropy group inwhich the scanning is skipped may be set equal to zero.

Referring to FIG. 15(b), the residual block is composed of a firstentropy group including a top-left residual coefficient, a secondentropy group located at the center, and a third entropy group includinga bottom-left residual coefficient. Based on the second information, thesecond entropy group may be determined as an entropy group including thestarting position of scanning. In this case, scanning is performed fromthe second entropy group, and the residual coefficient of the thirdentropy group may be set equal to zero.

Alternatively, the starting position of scanning may be determinedthrough a combination of the first information and the secondinformation. That is, one of a plurality of entropy groups may bespecified based on the second information, and a starting position inthe specified entropy group may be specified based on the firstinformation. Further, FIG. 15 does not limit the number, size or shapeof entropy groups, and the number of the entropy groups may be four ormore, and the shape of the entropy group may have a square or anon-square.

FIG. 16 illustrates a method of processing residual coefficients of apartial area in a residual block according to an embodiment of thepresent invention.

The encoding apparatus may perform a transform and/or quantization onthe residual samples of the residual block to derive residualcoefficients. At this time, the residual coefficient of the partial areain the residual block may not be entropy-encoded, and only the residualcoefficient of the remaining area may be entropy-encoded and transmittedto the decoding apparatus.

The decoding apparatus may decode only the residual coefficienttransmitted from the encoding apparatus and set the residual coefficientof the partial region as a pre-defined default value in the decodingapparatus. The default value may include at least one of an absolutevalue (abs) of a residual coefficient or a sign. The absolute value maybe zero, or may be a value greater than or equal to two or three.

Hereinafter, a method for determining the partial area in the decodingapparatus will be described.

Referring to FIG. 16, the partial area (gray area) may be an areaexcluding at least one of N columns from the left side or M rows fromthe top side in the residual block. Alternatively, the partial area maybe an area excluding the N×M area in the residual block.

The N and M may be a value pre-defined in the encoding/decodingapparatus or may be variably determined according to the size/type ofthe residual block. For example, when the residual block is 64×32, anarea excluding the 32 columns (where N=32, M=0) from the left side ofthe residual block may be defined as a partial area. When the residualblock is 32×64, an area excluding 32 rows (where N=0, M=32) from the topside of the residual block may be defined as a partial area. However,the values of N and M are only examples. N may be an integer greaterthan or equal to half the width (W) of the residual block, and M may bean integer greater than or equal to half the height (H) of the residualblock.

Alternatively, the N and M may be derived based on information encodedto specify a partial area. For example, the residual block may bedivided into a predetermined sub-area (e.g., a triangle, a rectangle, asquare, or any other shape). The index or coordinate information of thesub-area corresponding to the partial area may be encoded and signaled.Alternatively, the index of the sub-area corresponding to the N×M areamay be encoded and signaled, or the coordinate information specifyingthe size/shape of the N×M area may be encoded and signaled.

Specifically, the residual block may be divided into k sub-areas, basedon at least one of a vertical line or a horizontal line. The value k maybe an integer of 2, 3, 4 or more. The value k may be a fixed valuepre-defined in the encoding/decoding apparatus, or may be variablydetermined based on the vertical/horizontal line. An index may beassigned to each sub-area. Here, the index may be a value of 0 to (k−1).In this case, the index of the sub-area corresponding to the partialarea illustrated in FIG. 16 may be signaled, or the coordinateinformation of the sub-area corresponding to the partial area may besignaled. Conversely, the index of the sub-area corresponding to the N×Marea, which is an area where the residual coefficient is encoded andtransmitted by the encoding apparatus, may be signaled, or thecoordinate information specifying the size/shape of the N×M area may besignaled.

Alternatively, information indicating either the x-coordinate or they-coordinate of the coordinates (N, M) may be encoded and signaled. Inthis case, the partial area may be determined as one of a first groupincluding the residual coefficient with a position of (x1, y1) (whereN=<x1<W, 0=<y1<H), a second group including the residual coefficientwith a position of (x2, y2) (where 0=<x2<W, M=<y2<H) or a third groupincluding the residual coefficient with a position of (x3, y3) (whereN=<x3<W, M=<y3<H).

Alternatively, information indicating the coordinates (N, M) may beencoded and signaled. In this case, a group of residual coefficients,which is located at the right and bottom sides of thevertical/horizontal line passing through the coordinates (N, M), may bespecified, and the specified group may be determined as the partialarea.

In the above-described embodiment, the partial area may be determinedbased on at least one of the encoded information, and the residualcoefficient of the partial area may be set to a pre-defined defaultvalue. For the N×M area of the residual block, the residual coefficientderivation method described in FIG. 5 and FIGS. 12 to 15 may be applied.

Meanwhile, the process of setting the residual coefficient to a defaultvalue may be selectively performed in consideration of at least one ofthe size or the shape of the residual block. For example, the aboveprocess may be applied only when the size of the residual block isgreater than or equal to a predetermined threshold value. The size ofthe residual block may be expressed by at least one of the width or theheight of the residual block. The threshold value may mean the minimumsize at which it is allowed to set the residual coefficient to a defaultvalue (e.g., 0). The threshold value may be a value pre-defined in theencoding/decoding apparatus, or may be encoded and signaled by theencoding apparatus. The threshold value may be 32, 64, 128, 256, ormore.

The process of setting the residual coefficient to a default value maybe selectively performed based on flag information. The flag informationmay indicate whether to set the residual coefficient of the partial area(e.g., high frequency area) in the residual block to a default value.The flag information may be derived in the decoding apparatus based onthe size/shape of the residual block, or may be encoded and signaled bythe encoding apparatus.

However, the above process may be limited to be performed only when theresidual block is not encoded in the transform skip mode. Therefore,when the residual block is encoded in the transform skip mode, theencoding apparatus may not encode information necessary for setting theresidual coefficient to a default value.

Although the exemplary methods of this disclosure are represented by aseries of acts for clarity of explanation, they are not intended tolimit the order in which the steps are performed, and if necessary, eachstep may be performed simultaneously or in a different order. In orderto implement the method according to the present disclosure, theillustrative steps may additionally include other steps, include theremaining steps except for some steps, or may include additional stepsother than some steps.

The various embodiments of the disclosure are not intended to beall-inclusive and are intended to illustrate representative aspects ofthe disclosure, and the features described in the various embodimentsmay be applied independently or in a combination of two or more.

In addition, various embodiments of the present disclosure may beimplemented by hardware, firmware, software, or a combination thereof.In the case of hardware implementation, the hardware may be implementedby one or more application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), general processor, a controller, a micro-controller, amicro-processor, and the like.

The scope of the present disclosure includes a software ormachine-executable instructions (e.g., operating system, applications,firmware, program, etc.) which makes operations according to the methodsof the various embodiments be performed on the apparatus or computer anda non-transitory computer-readable medium, in which such software orinstructions are stored, executable on the apparatus or computer.

What is claimed is:
 1. A method of decoding a video signal, with adecoding apparatus, comprising: deriving, with the decoding apparatus, aresidual coefficient of a residual block, the residual block beingdivided into one or more entropy groups, a number of entropy groups inthe residual block being n, n being determined based on informationsignaled from an encoding apparatus; calculating, with the decodingapparatus, a quantization parameter for the residual block; performing,with the decoding apparatus, a dequantization on the residualcoefficient by using the calculated quantization parameter; andreconstructing, with the decoding apparatus, a residual sample of theresidual block by performing an inverse-transform on the dequantizedresidual coefficient, wherein the entropy groups are distinguished basedon a plurality of position information including position information ofa first residual coefficient and position information of a secondresidual coefficient, wherein the position information of the firstresidual coefficient is signaled at at least one level of a videosequence, a picture, a slice or a block, and the position information ofthe second residual coefficient is derived based on the positioninformation of the first residual coefficient, wherein the residualcoefficient of the residual block is derived through a scanningaccording to a scan order pre-defined in the decoding apparatus, whereinthe scan order is one of a zig-zag scan, a z-scan, an up-right diagonalscan, a bottom-left diagonal scan, a horizontal scan, and a verticalscan, wherein when the residual block includes a plurality of entropygroups, the scanning is performed by using a different scan order foreach entropy group, and wherein the scan order is determined based oninformation specifying the scan order of the residual block, theinformation being signaled, from the encoding apparatus, for eachentropy group.
 2. The method of claim 1, wherein at least one of a scanorder, an entropy decoding scheme, or a binarization scheme relating toa first entropy group is different from that of a second entropy group.3. The method of claim 1, wherein the scanning is performed from apre-determined starting position within the residual block.
 4. Themethod of claim 3, wherein the starting position is determined based onat least one of information indicating a starting position of thescanning or information specifying an entropy group including a startingposition of the scanning.
 5. The method of claim 1, wherein deriving theresidual coefficient further comprises setting a residual coefficient ofa partial area in the residual block to a default value pre-defined inthe decoding apparatus, and wherein the partial area is an areaexcluding at least one of N columns from a left side of the residualblock or M rows from a top side of the residual block.
 6. The method ofclaim 5, wherein N and M are derived based on information encoded tospecify the partial area.
 7. The method of claim 1, wherein the residualblock is a block divided into a variable size or shape based on at leastone of a quadtree, a binary tree or a triple tree.
 8. A method ofencoding a video signal, with an encoding apparatus, comprising:obtaining, with the encoding apparatus, a residual coefficient of aresidual block by performing a transform and a quantization on aresidual sample of the residual block; and generating, with the encodingapparatus, a bitstream by encoding the residual coefficient of theresidual block, wherein generating the bitstream, determining, with theencoding apparatus, a number of entropy groups belonging to the residualblock; determining, with the encoding apparatus, a scan order for eachof the entropy groups; and encoding, with the encoding apparatus, thenumber of the entropy groups and the scan order for each of the entropygroups, wherein the residual block is encoded by dividing into one ormore entropy groups, wherein when the residual block includes aplurality of entropy groups, at least one of a scan order, an entropydecoding scheme, or a binarization scheme relating to a first entropygroup of the plurality of entropy groups is different from that of asecond entropy group of the plurality of entropy groups, wherein theentropy groups are distinguished based on a plurality of positioninformation including position information of a first residualcoefficient and position information of a second residual coefficient,wherein the position information of the first residual coefficient isencoded at at least one level of a video sequence, a picture, a slice ora block, and the position information of the second residual coefficientis derived based on the position information of the first residualcoefficient, wherein the residual coefficient of the residual block isencoded through a scanning according to a scan order pre-defined in theencoding apparatus, wherein the scan order is one of a zig-zag scan, az-scan, an up-right diagonal scan, a bottom-left diagonal scan, ahorizontal scan, and a vertical scan, and wherein when the residualblock includes the plurality of entropy groups, the scanning isperformed by using a different scan order for each entropy group.